1. Field of the Invention
The present invention relates generally to a progressive stamping die assembly apparatus, and more particularly to such an apparatus for the manufacture of stacks of interlocked laminae.
2. Description of the Related Art
The manufacture of parts comprising a stack of interlocked laminae, e.g., stators and rotors for electric motors, or cylindrical cores for ignition system coils such as those used in low voltage ignition systems having spark plug-mounted coils, is known in the art. Apparatuses and methods associated with such manufacture are disclosed, for example, in U.S. Pat. No. 5,755,023 and Pending U.S. patent application Ser. No. 09/152,979, filed Sep. 14, 1998, which are assigned to the present assignee, and the disclosures of which are expressly incorporated herein by reference. Prior art progressive stamping die assemblies in which a plurality of differently shaped laminae are formed from a common piece of strip stock material, which laminae are stacked to form the laminated part, provide a separate stamping die station for each punch and die which forms a lamina having a particular shape and/or size.
In certain applications it is desirable to have a stack of interlocked laminae which is long and slender, and which has a cross-sectional shape having lateral sides defined by the lamina outer edges which do not lie in a substantially common plane; such a stack does not provide a choke-engaging surface which extends substantially along the vertical height of the stack. For example, it is desirable to have an elongate, substantially cylindrically-shaped lamina stack, in which the first, bottommost lamina is narrower than the adjacent, overlying second lamina, which is narrower than the adjacent, overlying third lamina, and so on, with the middlemost lamina(e) defining the widest portion of the substantially circular cross section and subsequent adjacent, overlying laminae each having a reduced width as compared to its adjacent lamina, thus forming a circular cross section, with each of the laminae of the cylindrically-shaped stack interconnected. Notably, the stock material from which a lamina stack may be produced according to the present invention is thin, and the individual laminae stamped therefrom quite flexible. Because the individual laminae of such a stack are long, thin and flexible, and may also not have common choke-engaging edges, the individual laminae tend to inadequately support the stack in the choke opening, rendering the above-described automatic interlocking method unusable for manufacturing such stacks.
It is known to form interlock tabs in the laminae which extend below the generally planar lamina surface. As the laminae of a stack is added to the stack, in the choke passageway located at the blanking station of the die assembly, each interlock tab engages a corresponding slot in the next lower lamina of the stack, generally by the entire thickness of the tab. The choke passageway may contain a plurality of individual laminated parts, themselves stacked upon each other. The bottom lamina of a stack may have the interlock tabs blanked and removed to avoid interlocking the bottom lamina with the next lower lamina which forms the top lamina of the previous stack. The choke passageway is typically configured to generally match the outer perimeter of at least one (i.e., the widest) of the blanked laminae in a stack and may be slightly undersized relative to that at least one lamina, e.g., by 0.001 inch, so that the laminae will be firmly held and accurately positioned within the choke passageway or barrel. The laminae, after they are located in the choke passageway with an interference fit thereby provide backpressure or resistance which facilitates the entry of the interlock tabs of the next lamina when it is pressed into the choke passageway.
These die stations are generally arranged linearly along a die bed of fixed length. Introducing additional die stations into the bed may thus not be easily facilitated. Further, where great variation in lamination shape and/or size is desired, the required length of prior die assembly apparatuses may be substantial, thereby requiring a large facility to accommodate the apparatus.
What is needed is an apparatus and method for producing long, slender, interlocked stacks of flexible laminae in which the laminae are automatically stamped, stacked and interlocked, the stacks having cross-sectional shapes with side surfaces defined by the side edges of the laminae which may or may not commonly engage the adjacent choke surfaces.
The present invention provides a method of manufacturing a stack of laminae in a progressive stamping die assembly having a choke passageway, means for guiding strip stock material through the die assembly in a first direction, and a transversely moveable die station which is moveable in opposite second and third directions substantially perpendicular to the first direction and having a plurality of predetermined positions. The method includes the steps of: stamping a first lamina having a first shape in the strip stock material in the transversely moveable die station while the transversely moveable die station is in a first predetermined position; substantially simultaneously advancing the strip stock material through the die assembly in the first direction and moving the transversely moveable die station in one of the second and third directions to a second predetermined position; stamping a second lamina having a second shape in the strip stock material in the transversely moveable die station while the transversely moveable die station is in the second predetermined position, the second shape different than the first shape; separating the first lamina from the strip stock material; placing the first lamina into the choke passageway; separating the second lamina from the strip stock material subsequently to placing the first lamina into the choke passageway; placing the second lamina into the choke passageway; and frictionally engaging the choke passageway with at least one of the first and second laminae.
The present invention also provides a progressive stamping die assembly apparatus for manufacturing a stack of laminae from strip stock material, the apparatus including means for incrementally advancing strip stock material through the die assembly apparatus in a first direction, and a transversely moveable die station comprising a plurality of matched punch and die hole sets arranged along opposite second and third directions, the second and third directions substantially perpendicular to the first direction. The transversely moveable die station has a plurality of preselected positions along the second and third directions, a different one of the plurality of matched punch and die hole sets interfaced with the strip stock material in each of the preselected transversely moveable die station positions. Different ones of the preselected transversely moveable die station positions are assumed by the transversely moveable die station substantially simultaneously with the strip stock material assuming an incrementally advanced position in the first direction through the die assembly apparatus.
An advantage of the present invention is that it provides the ability to easily introduce stamping variations without adding to the length of the apparatus.
Another advantage of the present invention is that it provides a shorter apparatus vis-a-vis previous apparatuses which produce similar laminated parts, thereby facilitating attendant facility requirement reductions.
Yet another advantage of the present invention is that, in addition to providing improved ability to introduce stamping variations without adding to the length of the apparatus, indeed, while providing a shorter apparatus, it is comparable in speed to previous progressive stamping die assembly apparatuses. The apparatus of the present invention can achieve 300 to 350 punch strokes per minute while presenting different die tools to the strip stock material between strokes.